The invention concerns a rolling parallel printer of the type comprising a plurality of type wheels which are arranged side-by-side on one common shaft, the shaft being fastened to a frame. The wheels can be set at specific positions. A pressure unit performs one periodic swiveling motion per printing cycle and forces the paper strip and the ribbon against the positioned line of types to accomplish the printing. A power drive produces the swiveling motion of the pressure unit.
Two different types of printers have recently been developed, and have become the most important designs for printing, on paper strips, data produced by electronic desk computers.
One of these types is the parallel printer with a reciprocating platen. Printing on the paper strip is accomplished in that the strip and an ink ribbon are pressed by the platen against the type wheels which are set at the specific digit positions.
The second type is the rolling printer wherein a platen of relatively small diameter, its center axle being linked to lever arms, is pivotably driven around a fixed axis. At one point of its rotary path a section of the perimeter of the platen rolls over the sandwiched paper strip and ribbon and the positioned types, in a planetary-type motion.
These two types of printers have both advantages and disadvantages. In case of the first-mentioned type the time required for the printing is short and the required traverse of the swivel can be accomplished in a simple manner by a mechanical drive mechanism. It is also possible to place the platen in its position of rest at such distance from the location of the type wheels that the printed data can be read with ease, while on the other hand a clear print-out requires a very heavy contact pressure which is particularly difficult to attain if carbon copies are needed. The high contact pressure demands not only a relatively strong motive power but also generates an annoying noise. Also, such pressure results in heavy stresses and wear and tear of the mechanical components, especially at the points of bearing and support. One additional advantage is due to the fact that the movements for the feed of the paper and the advance of the ribbon can be coordinated with the movement of the platen in a simple manner.
The known rolling printer, i.e., the second type, on the other hand requires a contact pressure of much lesser strength and produces copies of superior quality, but its printing consumes more time. It requires a relatively large space for the turning of the platen and the visibility of the print-out is poor unless auxiliary steps are introduced, namely backing up the paper by one line prior to the printing and advancing it by two lines after the printing, a procedure which requires a relatively complicated mechanical arrangement.
It is an object of the invention to design a rolling parallel printer in such manner that the disadvantages of the above-described parallel printers will be overcome to a great extent.
It is another object of the invention to provide a rolling printer of the kind which makes use of its superior feature, viz., pressing by means of a pressure unit against the ribbon and the paper, located in front of the positioned line of types in an automatically controlled motion which during the imprint phase accomplishes a rolling operation so that the magnitude of the contact forces can be held to a low value, while at the same time providing good visibility of the printed line.
It is a further object of the invention to provide such a rolling printer wherein despite a relatively wide route traveled by the pressure unit, from the instant of pressure to its position of rest, the travel actually performed by it, is relatively small due to a flattened path of travel.